A decomposable laminectomy punch, in which the two punch shafts, namely a punching bar and a punching slide, comprise straight, rod-shaped bodies each, which are mutually guided at one another, in the customary manner, by guide elements having a T-shaped profile that engage one another in a positive-locking manner, is known from an inhouse publication of the applicant. The rear end of the punching bar is provided here with a cylindrical mounting part, which has a larger diameter and has on its front side an annular stop shoulder, with which it is in contact with an axial stop, which is designed as a ring shoulder and in which the rearward ends of both punch shafts are mounted.
The movable punching slide is connected in an articulated manner to a pin-like plunger, which passes through a central axial hole of the guide part. At its rear end, this plunger has a pushing head, whose diameter is expanded and at which the short lever arm of the actuating lever for actuating the punching slide acts against the action of a restoring spring designed as a compression coil spring arranged on the plunger when the actuating lever is actuated. Locking depressions for a ball notch, which are arranged in a uniformly distributed manner, are provided on the circumference of the cylindrical mounting part. The two punch shafts can be rotated together in the tubular guide part and locked in a locking manner in different angular positions by means of this ball notch.
To make it possible to remove the two punch shafts together from the guide part, e.g., for cleaning purposes, it is necessary to remove the short lever arm of the actuating lever from the path of motion of the plunger. The actuating lever is mounted for this purpose with the short lever arm radially displaceably in relation to its bearing axis and with a special, axially stepped bearing journal, which can in turn be displaced against spring pressure in a bearing bore. The two punch shafts can then be pulled out of the guide part on the rear side together with the plunger and the restoring spring. These two parts can then be separated from one another by releasing the guide elements profiled in a T-shaped manner by correspondingly displacing the punching slide in the longitudinal direction relative to the punching bar.
This type of decomposability can be applied in case of straight punch shafts only, which can be pushed over their entire length through the tubular guide part. This type of decomposability cannot be used in case of punch shafts bent at right angles.
Another surgical bar shaft instrument, in which both grip parts are fixed together to a tubular guide part in an articulated manner and can be locked, is also known from DE 198 52 682 C2. By releasing the bolted connection, the two lever arms and especially the short lever arm of the actuating lever can be pivoted out of the path of movement of the two punch shafts, so that these can be pulled out of the guide part on the rear side.
This type of decomposability cannot be used in the case of punch shafts having a bent offset portion, which can be offset at right angles, either.